An internal combustion engine used in a motor vehicle or the like converts a reciprocating motion of a piston obtained by an explosive power of a fuel into a rotational motion by a connecting rod and a crank shaft, thereby obtaining a rotational driving force. The piston, the connecting rod and the crank shaft are connected by a piston pin and a crank pin. Further, the piston pin and the crank pin are borne by a slide bearing, and each of the slide bearings is repeatedly exposed to a variable load from the piston pin or the crank pin corresponding to an opposing shaft.
The slide bearing is generally structured such that an oil film is formed between the slide surface and the opposing shaft by supplying a lubricating fluid from an external portion so as to prevent a metal contact which is in direct contact with the opposing shaft from being generated. However, in the case that the opposing shaft slides with respect to the slide surface while applying the variable load to the slide surface, such as the slide bearing of the internal combustion engine mentioned above, the oil film is broken down and the metal contact tends to be generated, thereby causing a seize. In the case of the slide bearing which is used under an environment in which the oil film breakage is likely to be generated, it is preferable to improve a lubricating fluid keeping performance of the slide surface in such a manner that the lubricating fluid is excluded from the slide surface so as to prevent the oil film from being broken down even if the variable load is applied from the opposing shaft.
As the slide member in which the lubricating fluid keeping performance is improved, there exists a structure described in JP-A-2002-147459 (patent document 1). This structure is made such that an overlay layer is attached onto a bearing alloy layer, and hard micro particles are sprayed to the overlay layer in accordance with a shot blast so as to form micro concave portions on a surface of the overlay layer corresponding to the slide surface, thereby improving an oil keeping performance.
In the slide member described in the patent document 1, since the concave portion is formed on the overlay layer in accordance with a plastic deformation, a periphery thereof bulges (the bulged portion is called as a bank portion). Since a load is concentrated to the bank portion and a problem that the bank portion tends to seizure, a height of the bank portion is lowered by applying a polishing work such as a barrel finishing or the like after the shot blast. However, a after finishing such as the polishing work is required in this case, and a manufacturing cost is increased.
Further, since the concave portions are formed in accordance with the shot blast, the formed concave portions are partly overlapped with each other so as to be in a state in which the concave portions are connected to each other. Accordingly, when the opposing member presses the slide surface at a high load, the lubricating fluid flows out from the concave portion to the concave portion, so that the lubricating fluid runs away from the slide surface, and it is undesirable to improve the oil keeping performance.